Image amplifier



Filed Jan. 25, 1955 iNVENTOR Edward L. Webb ATTORNEY WITNESSES Uni ed S a v Pat IMAGE AMPLIFIER Edward L. Webb, Baltimore, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 25, '1955, Serial No. 484,002

7 Claims. (Cl. 250-213) My invention relates to radiation image amplifiers and, in particular, to a novel type of image intensifier which makes use of the combined properties of photoconductors and gaseous electrical discharge to eifect its purposes. I illustrate it here by applying its broad principles to an intensifier and converter of images of X-ray or other types of radiation.

One object of my invention is to provide a novel arrangement for producing visible light images which duplicate the spatial distribution of radiation fields.

Another object is to provide a novel arrangement for producing gaseous discharges which have intensity distributions which are replicas of the intensity distributions of radiation fields.

Another object is to convert X-ray images into visible light images by a novel and effective method.

Another object is to produce an electrical discharge distribution which duplicates the area distribution of varying electrical conductivity in a photoconductor.

Another object is to provide a novel form of radiation image intensifier which is simple, compact and of low first cost. 7

Other objects of my invention will become apparent upon reading the following description taken in connection with the drawings, in which:

Figure 1 is a schematic mid-sectional view of an electrical discharge device applying the principles of my invention to X-ray image conversion; and

Fig. 2 is a similar view of a modified form for such a device.

Referring in detail to the drawings, a vacuum-tight container 1 having substantially planar end faces carries a first electrode in the form of a layer 2 of transparent conducting material such as may be formed from SnO in ways well known in the art. The free face of layer 2 is covered with a layer 3 of a photoconductive material such as cadmium sulphide. The other planar end of container 1 bears a second electrode in the form of layer 4 of transparent conductive material also. The container 1 has a filling of gas which is chemically inert to the photoconductive layer 3 and end layer 4 at a pressure preferably such that the mean-free path is at least equal to the distance between layers 3 and 4. This gas may, for example, be at a pressure of substantially 0.01 to 10 mm. of Hg if the layers 3 and 4 are respectively cadmium sulphide and SnO Inleads 5 and 6 enable electric currents to flow from layers 2 and 4 to an external circuit containing a direct current source 7 and a current-limiting resistor 8.

While I have described the principles of my invention as carried out in a tube employing a photoconductive layer 3, the latter may be replaced by a layer of material which is rendered temporarily conductive in the vicinity of the incidence point of any sub-atomic particle such as an electron, proton, neutron or alpha particle; i.e. by what may be termed a bombardment-sensitive conductor. In such case, the X-rays would, of course, be replaced by an image-field of such sub-atomic particle, and the container wall-portion be transparent thereto.

The voltage of source 7 would be made such that a luminous discharge would pass through the gas opposite those points of the layer 3 as were rendered conductive by photon or particle incidence, but remained non-luminous opposite points where no particles were incident. The luminosity of the gas would thus vary moment by moment opposite each point of the area of layer 3 in substantial proportion to the fluctuations in intensity of the incident radiation field.

It will, in many cases, be possible to employ a gaseous atmosphere having a luminosity of such wavelength as not to afiect the photoconductive layer 3; thereby avoiding any feed-back and instability; but where such is not the case, a light shield may be provided between the luminous gas and the layer 3. This light shield should conduct electricity in a direction normal to the planar face of layer 3, but not substantially parallel thereto. For example, a thin high-resistivity film of some material such as graphite particles may be deposited in contact with the outside of layer 3.

A modification of the Fig. 1 arrangement which would give higher light output in some fields appears in Fig. 2. In this arrangement, the gaseous atmosphere selected is one such as mercury vapor, or argon which would generate ultraviolet radiation in the glow discharge. A fluorescent screen 9 is deposited over conductive layer 4 and is stimulated to luminosity point-by-point over its area by the ultraviolet radiation.

Where it was desired to employ an intensifier for ultraviolet radiation image-fields, the photoconductor layer 3 might be of a material such as cadmium sulphide, arsenic trisulphide or amorphous selenium which was efficiently sensitive to visible light, and to provide an additional input screen 11 of fluorescent material which generated visible light under stimulus of ultraviolet irradiation. Such a tube could also be used for X-ray or other input-radiation fields by employing a screen 11 which responded with visible light to stimulation by said input radiation.

I claim as my invention:

1. An X-ray image intensifier comprising a vacuumtight envelope having a wall portion which is substantially transparent to X-rays, a conductive X-ray transparent layer between said wall portion and a substantially planar layer of material which is rendered temporarily more conductive in the vicinity of an incident X-ray photon, a light-transparent conductive layer spaced from said planar layer, in-leads through said envelope for said X-ray transparent layer and said light-transparent conductive layer, and a gaseous atmosphere of substantial pressure within said envelope.

2. The X-ray image intensifier specified in claim 1 in which said planar layer material is cadmium sulphide.

3. The image intensifier specified in claim 1 in which the gaseous atmosphere comprises helium, neon, argon, krypton, mercury vapor, etc., or mixtures thereof.

4. An image converter which comprises a vacuumtight envelope having an input screen comprising a conductive layer having a substantially planar surface of bombardment-sensitive material spaced away from a transparent conductive layer, in-leads for said planar surface and said conductive layer sealed through said envelope, and a gaseous atmosphere therein.

5. The image intensifier specified in claim 1 in which said conductive layer is coated with a fluorescent layer.

6. An image converter which comprises in combination a vacuum-tight envelope, a first substantially planar and substantially transparent electrode within said envelope, a substantially planar layer of photoconductive material for receiving a spatial radiation image and control ionization in said gas so as to generate a luminous discharge image having the pattern of said radiation image. V

7. The apparatus of claim 6 in which said first electrode and said second electrode are connected to an external source of electrical potential.

References Cited in the iile of'this patent UNITED STATES, PATENTS 1,724,298 Miller Aug. 13, 1929 2,120,765 Orvin June 14, 1938 2,258,294 Lubszynski Oct. 7, 1941 2,605,335 Greenwood et al July 29, 1952 2,824,986 Rome Feb. 25, 1-958 

